Large, inhalable particles are present in the workplace, yet few instruments exist to count and size such particles in situ. Inhalable aerosol exposure can be evaluated using mass-based samplers such as the IOM or Button sampler, but these devices do not provide information on particle size distributions. Size-resolved samplers such as cascade impactors or the Aerodynamic Particle Sizer are limited to particle sizes<20 micrometers (μm) due to difficulties with particle aspiration and transmission losses.
Inhalable particles are defined as those that penetrate into the head airway region and beyond. Ogden and Birkett (Ogden and Birkett 1975) were the first to present the idea of the human head as a blunt aerosol sampler and to demonstrate that the head does not effectively inhale particles of all sizes. The inhalable particulate mass (IPM) criterion was subsequently developed to describe the fractional sampling efficiency of the human head (the inhaled fraction, or IF) as a function of particle aerodynamic diameter:IF=0.5*(1+exp(−0.06*dae)  (1)for wind speeds<4 m s−1 and particles<100 μm (Soderholm 1989).
Exposure to inhalable aerosols is traditionally assessed using time-integrated personal samplers with gravimetric analyses to determine dust concentration (Eller and Cassinelli 1994). The 37-mm cassette is the most commonly used personal sampler in the US for industrial hygiene sampling. However, the 37-mm cassette under-samples large particles (>20 μm), relative to the human head (Kenny et al. 1999; Kenny et al. 1997). Compared with the 37-mm cassette, the IOM and Button samplers have sampling efficiencies that better match the IPM criterion (Grinshpun et al. 1995; Kalatoor et al. 1995; Mark and Vincent 1986). All of these size-selective samplers are limited; they do not report size distributions, only mass concentrations. Instruments capable of reporting the size distribution of aerosols exist, such as the Aerodynamic Particle Sizer (APS), Scanning Mobility Particle Sizer (SMPS) and various cascade impactors; however, these instruments are limited to particle sizes less than about 20 μm in aerodynamic diameter.
The aerodynamic particle sizer (APS) reports concentration and size distribution for airborne particles from 0.5 to 20 μm and has been extensively used in laboratory and field studies (Armendariz and Leith 2002; Baron 1986; Chen et al. 1985; Görner et al. 2010; Marshall et al. 1991; Peters et al. 2006). Although extremely useful, the APS provides size distribution information for only a fraction of the inhalable range. At approximately 10 μm, the APS begins to experience issues with particle transmission efficiency into the detector (Volckens and Peters 2005).
Gibson, Vincent and Mark (Gibson et al. 1987) developed the personal inhalable dust spectrometer (PIDS), an eight-stage, cascade impactor with an entry designed to match the IPM criterion. The PIDS has been used to characterize the size distribution of aerosol particles in coal mines, bakeries, and primary lead smelters, where most of the mass is coarse. Mass median diameters of 41.6, 60.7, 67.3 and 71.4 μm were found in ore storage and milling, sinter pants, blast furnace, and drossing areas, respectively (Spear et al. 1998). Bimodal distributions were found in an automated bakery, egg powdery, cement factory, steel mill, spice factory, and in furniture carpentry, with large mass median diameters for the coarser mode ranging from 14-59 μm (Lidén et al. 2000). These studies demonstrate the presence of coarse dust in workplaces, with mass median diameters often above 40 μm.
Although the measurement of inhalable particles is difficult, accurate knowledge of their concentration and size is necessary to assess exposure and dose. Substantial differences exist in deposition to the oral, nasal, pharyngeal and laryngeal regions for particles between 10 and 50 μm (Cheng et al. 1999); thus, the health effects of these particles can be substantially different. Particle deposition in the tracheobronchial region could potentially cause health effects such as asthma and bronchogenic cancer. Particles depositing in the oronasal cavities could result in health effects centered primarily in the upper respiratory region.
A high prevalence of occupational illnesses is related to inhalable-particle exposures. For example, occupational rhinitis occurs three times more frequently in occupational settings than occupational asthma (Bush et al. 1998). Exposure to animal dander (Kup 1985; Slovak and Hill 1981), flours (Moscato et al. 2008), wood dust (Kanerva and Vaheri 1993; Moscato et al. 2008), textile dust (Slavin 2003), food, spices, organic dusts, latex and chemicals have all been associated with occupational rhinitis, as has exposure to pesticides (Slager et al. 2009). Furriers, spice workers, vegetable pickers, hemp workers, and grain handlers all have increased prevalence rates for self-reported sinusitis (El Karim et al. 1986; Zuskin et al. 1990; Zuskin et al. 1993; Zuskin et al. 1988a; b).
Sinonasal tumors are rare, but of all cancers have the second highest fraction attributable to occupational exposures (Rushton et al. 2012; Youlden et al. 2013). Exposure to wood dust (Andersen et al. 1977; Kleinsasser and Schroeder 1988; Pesch et al. 2008; WHO 1995), leather dust (Bonneterre et al. 2007), nickel compounds, radium-226, radium-228 and their decay products, and acids used in isopropyl alcohol production are all known risk factors for sinonasal cancer (Baan et al. 2009; El Ghissassi et al. 2009; Straif et al. 2009). Textile dust (Luce et al. 1997) and hexavalent chromium are possible risk factors for sinonasal tumors as well, but evidence is limited.
Retrospective epidemiological studies, exposure assessments, and the design of industrial hygiene controls are all hindered by this inability to monitor inhalable particles accurately. The objective of this study, therefore, was to develop a particle separator capable of characterizing concentrations and size distributions of inhalable aerosol particles from 30 to 100 μm in aerodynamic diameter. The designs described here focus on sampling in calm air environments, as mean indoor wind speeds are generally less than 0.3 m s-1 in most workplaces (Baldwin and Maynard 1998).